Tooling and methods for circumferential friction stir welding

A back-up tooling apparatus for backing up an inner surface of a hollow cylindrical workpiece to be friction stir welded along a circumferential weld path, comprising:

• a plurality of shoes each having an outer surface that is arcuate in a circumferential direction of the workpiece, the shoes being configured to mate end-to-end with one another so as to form a substantially continuous ring having an outer diameter approximately equal to a diameter of the inner surface of the workpiece;
• and
• a radially expandable support having a plurality of support arms respectively attached to the plurality of shoes, the expandable support being operable to extend the support arms and shoes outwardly to cause the shoes to mate with one another in end-to-end relation to form said continuous ring and to urge the shoes against the inner surface of the workpiece, wherein mating end portions of circumferentially adjacent shoes are configured to overlap in the circumferential direction when the shoes are expanded to form the ring such that weld pressure exerted radially inward on the overlapping end portions causes the overlapping end portions to be forced together.

A back-up tooling apparatus for backing up an inner surface of a hollow cylindrical workpiece to be friction stir welded along a circumferential weld path, comprising:

• a plurality of shoes each having an outer surface that is arcuate in a circumferential direction of the workpiece, the shoes being configured to mate end-to-end with one another so as to form a substantially continuous ring having an outer diameter approximately equal to a diameter of the inner surface of the workpiece, each shoe being in contact with shoes on either side thereof;
• the shoes being alternately configured to become circumferentially narrower and wider in a radially outward direction to form an interlocking arrangement such that force exerted radially outward on a narrowing shoe is transmitted to adjacent widening shoes, and wherein inward-facing end faces of the widening shoes overlap outward-facing end faces of adjacent narrowing shoes, and further comprising a seal material disposed between the overlapping end faces.